Prosthetic pylon having an enclosed compressible volume of fluid to support a patient&#39;s weight

ABSTRACT

A pylon includes a first end portion connected to a patient&#39;s leg stump and a second end portion connected to a prosthetic foot. The second end portion includes a piston, and the first end portion includes a piston chamber receiving the piston. The second end portion is thus rotatable and axially movable relative to the first end portion about and along a longitudinal axis of the pylon, respectively. The piston chamber encloses a compressible volume of fluid through which substantially all of the patient&#39;s weight applied through the patient&#39;s leg stump is supported. The compressible volume of fluid is sealed so that it can be pressurized. Also, a torsional spring couples the piston and piston chamber and resists relative rotation between the piston and piston chamber without supporting any substantial portion of the patient&#39;s weight applied through the patient&#39;s leg stump to the piston. The present invention thus advantageously provides a pylon which is more cushioned and resilient than conventional pylons.

TECHNICAL FIELD

The present invention relates in general to a prosthetic pylon, and inparticular to a prosthetic pylon supporting the weight of a patient onan enclosed compressible volume of fluid.

BACKGROUND OF THE INVENTION

Individuals who lose all or part of a leg have a residual leg stump towhich a prosthetic foot is often attached through an elongated pylon.Such a pylon is typically a rigid member made with a material, like acarbon-fiber composite or aluminum, which provides the rigiditynecessary to support an individual's weight.

This rigidity can be problematic, because it often makes conventionalpylons too stiff for comfortable movement. Each step on such a pylon canbe awkward and painful, rather than cushioned and resilient like anatural leg. Therefore, there is a need in the art for a pylon whichadequately supports an individual's weight and is more cushioned andresilient than conventional pylons.

SUMMARY OF THE INVENTION

An inventive pylon includes a first end portion connected to a patient'sleg stump and a second end portion connected to a prosthetic foot. Thesecond end portion is rotatable and axially movable relative to thefirst end portion about and along a longitudinal axis of the pylon,respectively. Preferably, the second end portion includes a piston, andthe first end portion includes a piston chamber receiving the piston.The piston chamber encloses a compressible volume of fluid through whichsubstantially all of the patient's weight applied through the patient'sleg stump is supported. The compressible volume of fluid is preferablysealed so that it can be pressurized. Also, a torsional spring couplesthe piston and piston chamber and resists relative rotation between thepiston and piston chamber without supporting any substantial portion ofthe patient's weight applied through the patient's leg stump. Thepresent invention thus advantageously provides a pylon which is morecushioned and resilient than conventional pylons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a prosthetic system using the inventivepylon.

FIG. 2 is a side cross-sectional view of the inventive pylon of FIG. 1.

FIG. 3 is a plan cross-sectional view of a torsional spring of theinventive pylon of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a preferred embodiment of the presentinvention provides a prosthetic system 10 comprising a prosthetic foot12 and a pylon 14. The pylon 14 has a first end portion 16 releasablyconnected to a conventional socket 18 into which a patient's leg stumpfits, and a second end portion 20 releasably connected to the prostheticfoot 12. The second end portion 20 is rotatable relative to the firstend portion 16 about a longitudinal axis 22 of the pylon 14, and is alsoaxially movable relative to the first end portion 16.

The pylon 14 of FIG. 1 is shown in more detail in FIG. 2. The first endportion 16 includes a conventional attachment plate 24 which attaches tothe conventional socket (not shown in FIG. 2) in a well known manner.The angle of the attachment plate 24 may be adjusted with adjustmentbolts 26.

The first end portion 16 also includes a piston chamber 28 receiving apiston 30. The piston chamber 28 is preferably made of aluminum ortitanium, and the piston 30 is preferably made of titanium.

The piston 30 has an O-ring seal 32 mounted in a groove about itscircumference so that the piston chamber 28 contains an enclosed, sealedarea 34. Alternatively, the piston chamber 28 can be enclosed and sealedby a membrane (not shown) attached to the inner walls of the pistonchamber 28 and positioned orthogonally to the longitudinal axis 22. Asanother alternative, the piston chamber 28 can include a fluid bladder(not shown) which is enclosed and sealed.

A retainer block 36 retains the piston 30 in the piston chamber 28, andO-ring bumpers 40 cushion the impact of the piston 30 against theretainer block 36. A bearing, such as a wear ring 44, is mounted aboutthe circumference of the piston 30 in contact with the inner walls ofthe piston chamber 28, and a beating such as a wear ring 48, is mountedin the retainer block 36 in contact with the piston 30. The wear rings44 and 48 are preferably made of TURCITE-X®, and will be discussed inmore detail below.

The pylon 14 also has a torsional spring including cushions (not shownin FIG. 2) and a torsion key 52 rotatably mounted at one end in abearing 54 seated in an interior end of the piston chamber 28. Thecushions and the torsion key 52 are retained by a stop plate 56. A slotin the head of the piston 30 receives the other end of the torsion key52 in a torsion slide 58 preferably made of TURCITE-X®. As a result, thetorsion key 52 slides into and out of the head of the piston 30 withlittle resistance, but it is forced to rotate in its bearing 54 againstthe cushions (not shown in FIG. 2) about the longitudinal axis 22 whenthe piston 30 rotates relative to the piston chamber 28. The torsion key52 and cushions will be described in more detail below.

In operation, the area 34 contains a compressible volume of fluid,preferably air. However, the fluid can also be, for example, anothercompressible gas or an incompressible liquid containing compressibleobjects. Those having skill in the field of this invention willunderstand that a wide variety of compressible volumes of fluid failwithin the scope of this invention. Also, it is preferable that thepylon 14 include a fitting 60 so that the compressible volume of fluidcan be pressurized. This allows a patient to customize the response ofthe pylon 14.

As the patient moves forward, the heel of the prosthetic foot (not shownin FIG. 2) strikes the ground. At this time, a force F_(w) due to thepatient's weight is impressed on the piston 30, and the piston 30 slidesinto the piston chamber 28 resisted by a pressure force F_(P) as thecompressible volume of fluid compresses. As a result, substantially allof the patient's weight applied to the piston 30 is resilientlycushioned by the compressible volume of fluid. At the same time, thetorsion key 52 slides into the slot in the head of the piston 30. As thepatient continues forward, the patient's weight is transferred from theheel to a point forward on the prosthetic foot (not shown in FIG. 2)impressing a moment on the piston 30 relative to the piston chamber 28which may, for example, be resolved into a couple including a momentM_(w) centered on the wear ring 48 and a force F_(a), imposed on thewear ring 48. This moment M_(w) impresses a force F_(b) on the wear ring44, for example, as follows:

    F.sub.b =(M.sub.w /d.sub.b)                                (1)

where d_(b) is the length of the moment arm at the wear ring 44. Becauseof the coefficients of friction μ_(a), μ_(b) between the wear rings 48and 44 and the piston 30 and the inner wall of the piston chamber 28,respectively, the forces F_(a) and F_(b) cause the wear rings 44 and 48to resist motion by the piston 30 with a fiction force F_(F) equal to:

    F.sub.F =(μ.sub.a *F.sub.a +μ.sub.b *F.sub.b)        (2)

At a point during the patient's movement forward when the toes of theprosthetic foot (not shown in FIG. 2) are on the ground and the heel isbeginning to rise, the moment M_(w) and the force F_(a), reach theirmaximum.

At this point in the patient's gait, the pressure force F_(P) tries tourge the piston 30 out of the piston chamber 28, but the fiction forceF_(F) (which is at its maximum because of the maximized moment M_(w) andforce F_(a)) advantageously restricts motion by the piston 30.

When the moment M_(w) and the force F_(a) decrease from their maximumvalues as the patient continues forward, and the force F_(w) due to thepatient's weight lessens as the patient's weight shifts to the otherleg, the friction force F_(F) decreases sufficiently to allow thepressure force F_(P) to rapidly urge the piston 30 out of the pistonchamber 28. As a result, the patient receives an advantageous boostforward. The timing and amount of the boost can, of course, becontrolled by varying the pressurization of the compressible volume offluid through the fitting 60, by varying the length of the moment armd_(b), and by varying the coefficients of friction μ_(a) and μ_(b).

The torsion key 52 is shown in more detail in FIG. 3. It includesprojections 52a and 52b which compress cushions 64a, 64b, 64c, 64d whenthe torsion key 52 is rotated by the piston (not shown in FIG. 3) aboutthe longitudinal axis 22 of the pylon (not shown in FIG. 3). In thismanner, the torsion key 52 resists rotation by the piston, and hence bythe patient's leg stump (not shown in FIG. 3), about the longitudinalaxis 22. The cushions 64a, 64b, 64c, 64d are preferably made ofpolyurethane, and they allow a range of rotation by the torsion key 52of approximately ±15°.

In an alternative embodiment, the shapes, positions and spring rates ofthe cushions 64a, 64b, 64c, 64d may be selected so that the cushions64a, 64b, 64c, 64d resist clockwise rotation by the torsion key 52 witha different force than they resist counter-clockwise rotation. It may,for example, be advantageous to have a different resistance to clockwiseand counter-clockwise rotation according to whether the pylon (not shownin FIG. 3) is attached to a right or a left leg stump. Also, it will beunderstood that a wide variety of alternative configurations for thecushions are possible--including more or less than four cushions--andthat these alternative configurations fall within the scope of thepresent invention.

The present invention thus advantageously provides a pylon which iscushioned and resilient. It also provides a patient a boost forward atan advantageous moment in their stride.

Although the present invention has been described with reference to apreferred embodiment, the invention is not limited to this preferredembodiment. Rather, the invention is limited only by the appendedclaims, which include within their scope all equivalent devices ormethods which operate according to the principles of the invention asdescribed.

We claim:
 1. A pylon for supporting the weight of a patient with a legstump on a prosthetic foot supported by the ground, the pyloncomprising:a first end portion connectable to the patient's leg stump; asecond end portion opposing the first end portion and connectable to theprosthetic foot, the second end portion being rotatable and axiallymovable relative to the first end portion about and along a longitudinalaxis of the pylon, respectively, wherein one of the first and second endportions includes a piston having a head with a slot therein, whereinthe other of the first and second end portions includes a piston chamberwith an interior end facing the piston head and interior walls forreceiving the piston along the longitudinal axis of the pylon; anenclosed compressible volume of fluid coupling the first and second endportions and through which substantially all of the patient's weightapplied through the patient's leg stump to the first end portion issupportable, and wherein the compressible volume of fluid is enclosed bythe piston head and piston chamber; and a torsional spring coupling thefirst and second end portions for resisting relative rotation betweenthe first and second end portions without supporting any substantialportion of the patient's weight applied through the patient's leg stumpto the first end portion, wherein the torsional key comprises:a torsionspring having a first end rotatably mounted to the interior end of thepiston chamber so that the torsion key is rotatable about thelongitudinal axis of the pylon, the first end of the torsion key havingprojections extending radially from the rotation axis of the torsion keytoward the interior walls of the piston chamber, the torsion key havinga second end slidably engaging the piston head's slot so that relativerotation between the piston and the piston chamber rotates the torsionkey; and one or more cushions positioned at the interior end of thepiston chamber in close proximity to the projections at the first end ofthe torsion key so that the projections compress at least some of thecushions when relative rotation between the piston and the pistonchamber rotates the torsion key.
 2. A pylon for supporting the weight ofa patient with a leg stump on a prosthetic foot supported by the ground,the pylon comprising:a first end portion connectable to the patient'sleg stump; a second end portion opposing the first end portion andconnectable to the prosthetic foot, the second end portion beingrotatable and axially movable relative to the first end portion aboutand along a longitudinal axis of the pylon, respectively; an enclosedcompressible volume of fluid coupling the first and second end portionsand through which substantially all of the patient's weight appliedthrough the patient's leg stump to the first end portion is supportable;and a torsional spring coupling the first and second end portions forresisting relative rotation between the first and second end portionswithout supporting any substantial portion of the patient's weightapplied through the patient's leg stump to the first end portion,wherein the torsional spring is contained within the enclosedcompressible volume of fluid.
 3. The pylon of claim 2 wherein one of thefirst and second end portions includes a piston having a head, whereinthe other of the first and second end portions includes a piston chamberfor receiving the piston along the longitudinal axis of the pylon, andwherein the compressible volume of fluid is enclosed by the piston headand piston chamber.
 4. The pylon of claim 3 wherein the piston has aseal circumferentially mounted thereon so that the piston head andpiston seal together seal the portion of the piston chamber containingthe compressible volume of fluid.
 5. The pylon of claim 2 wherein thecompressible volume of fluid is enclosed and sealed so that it can bepressurized.
 6. The pylon of claim 2 wherein the compressible volume offluid comprises a compressible fluid.
 7. A pylon for supporting theweight of a patient with a leg stump on a prosthetic foot supported bythe ground, the pylon comprising:a first end portion connectable to thepatient's leg stump; a second end portion opposing the first end portionand connectable to the prosthetic foot, the second portion beingrotatable and axially movable relative to the first end portion aboutand along a longitudinal axis of the polygon, respectively; an enclosedcompressible volume of fluid coupling the first and second end portionsand through which substantially all of the patient's weight appliedthrough patient's legs stump to the first end portion is supportable,wherein the enclosed compressible volume of fluid is compressed duringheel strike of the prosthetic foot and is decompressed when thepatient's weight shifts during movement of the prosthetic foot; abearing interposed between the first and second end portions such thatit restricts the decompression of the enclosed compressible volume offluid until an appropriate moment in the movement of the prosthetic footwhen the decompression will assist the patient in accelerating forward;and a torsional spring coupling the first and second end portions forresisting relative rotation between the first and second end portionswithout supporting any substantial portion of the patient's weightapplied through the patient's leg stump to the first end portion.
 8. Thepylon of claim 7 wherein one of the first and second end portionsincludes a piston having a head, wherein the other of the first andsecond end portions includes a piston chamber for receiving the pistonalong the longitudinal axis of the pylon, wherein the compressiblevolume of fluid is enclosed by the piston head and piston chamber,wherein the bearing comprises a wear band interposed between sides ofthe piston and interior walls of the piston chamber such that itmomentarily restricts relative motion between the piston and the pistonchamber along the longitudinal axis of the pylon when a sufficientmoment is imparted to the piston relative to the piston chamber about alateral axis of the piston during the movement of the prosthetic foot.9. A pylon for supporting the weight of a patient with a leg prostheticfoot supported by the ground, the pylon comprising:a first end portionconnectable to the patient's legs stump; a second end portion opposingthe first end portion and connectable to the prosthetic foot, the secondend portion being rotatable and axially movable relative to the firstend portion about and along a longitudinal axis of the pylon,respectively; an enclosed compressible volume of fluid coupling thefirst and second end portions and through substantially all of thepatient's weight applied through the patient's leg stump to the firstend portion is supportable; and a torsional spring coupling the firstand second end portions for resisting relative rotation between thefirst and second end portions without supporting any substantial portionof the patient's weight applied through the patient's leg stump to thefirst end portion, wherein the torsional spring resists clockwiserotation with a first spring rate and wherein the torsional springresists counter-clockwise rotation with a second spring rate that isselected to be different than the first spring rate in accordance withthe patient's leg stump being either a right or left leg stump.
 10. Aprosthetic system for supporting the weight of a patient having a legstump, the prosthetic system comprising:a prosthetic foot; and a pyloncomprising:a first end portion connectable to the patient's leg stump; asecond end portion opposing the first end portion and connectable to theprosthetic foot, the second end portion being rotatable and axiallymovable relative to the first end portion about and along a longitudinalaxis of the pylon, wherein one of the first and second end portions ofthe pylon includes a piston having a head with a slot therein, whereinthe other of the first and second end portions of the pylon includes apiston chamber for receiving the piston along the longitudinal axis ofthe pylon, the piston chamber having an interior end facing the pistonhead and also having interior walls; an enclosed compressible volume offluid coupling the first and second end portions and through whichsubstantially all of the patient's weight applied through the patient'sleg stump to the first end portion is supportable, wherein thecompressible volume of fluid is enclosed by the piston head and pistonchamber; and a torsional spring coupling the first and second endportions for resisting relative rotation between the first and secondend portions without supporting any substantial portion of the patient'sweight applied through the patient's leg stump to the first end portion,wherein the torsional spring comprises:a torsion key having a first endrotatably mounted to the interior end of the piston chamber so that thetorsion key is rotatable about the longitudinal axis of the pylon, thefirst end of the torsion key having projections extending radially fromthe rotation axis of the torsion key toward the interior walls of thepiston chamber, the torsion key having a second end slidably engagingthe piston head's slot so that relative rotation between the piston andthe piston chamber rotates the torsion key; and one or more cushionspositioned at the interior end of the piston chamber in close proximityto the projections at the first end of the torsion key so that theprojections compress at least some of the cushions when relativerotation between the piston and the piston chamber rotates the torsionkey.
 11. A prosthetic system for supposing the weight of a patienthaving a leg stump, the prosthetic system comprising:a prosthetic foot;and a pylon comprising:a first end portion connectable to the patient'sleg stump; a second end portion opposing the first end portion andconnectable to the prosthetic foot, the second end portion beingrotatable and axially movable relative to the first end portion aboutand along a longitudinal axis of the pylon; an enclosed compressiblevolume of fluid coupling the first and second end portions and throughwhich substantially all of the patient's weight applied through thepatient's leg stump to the first end portion is supportable; and atorsional spring coupling the first and second end portions forresisting relative rotation between the first and second end portionswithout supporting any substantial portion of the patient's weightapplied through the patient's leg stump to the first end portion,wherein the torsional spring is contained within the enclosedcompressible volume of fluid.
 12. A prosthetic system for supporting theweight of a patient having a leg stump, the prosthetic systemcomprising:a prosthetic foot; and a pylon comprising:a first end portionconnectable to the patient's leg stump; a second end portion opposingthe first end portion and connectable to the prosthetic foot, the secondend portion being rotatable and axially movable relative to the firstend portion about and along a longitudinal axis of the pylon; anenclosed compressible volume of fluid coupling the first and second endportions and through which substantially all of the patient's weightapplied through the patient's leg stump to the first end portion issupportable, wherein the enclosed compressible volume of fluid iscompressed during heel strike of the prosthetic foot and is decompressedwhen the patient's weight shifts during movement of the prosthetic foot;a bearing interposed between the first and second end portions such thatit restricts the decompression of the enclosed compressible volume offluid until an appropriate moment in the movement of the prosthetic footwhen the decompression will assist the patient in accelerating forward;and a torsional spring coupling the first and second end portions forresisting relative rotation between the fast and second end portionswithout supporting any substantial portion of the patient's weightapplied through the patient's leg stump to the first end portion.
 13. Amethod for supporting the weight of a patient having a leg stump on aprosthetic foot supported by the ground, the methodcomprising:supporting the patient's leg stump on the prosthetic footthrough an enclosed compressible volume of fluid so that substantiallyall of the patient's weight supported on the prosthetic foot issupported by the enclosed compressible volume of fluid, wherein theenclosed compressible volume of fluid is compressed during heel strikeof the prosthetic foot and is decompressed when the patient's weightshifts during movement of the prosthetic foot; restricting thedecompression of the enclosed compressible volume of fluid until anappropriate moment in the movement of the prosthetic foot when thedecompression will assist the patient in accelerating forward; andresisting rotation of the patient's leg stump relative to the prostheticfoot about a longitudinal axis of the stump with a torsional springwithout supporting any substantial portion of the patient's weight withthe torsional spring.
 14. A pylon for supporting the weight of a patientwith a leg stump on a prosthetic foot supported by the ground, the pyloncomprising:a first end portion connectable to the patient's leg stump; asecond end portion opposing the first end portion and connectable to theprosthetic foot, the second end portion being axially moveable relativeto the first end portion along a longitudinal axis of the pylon; and acompressible medium coupling the first and second end portions andpositioned therebetween along the longitudinal axis of the pylon so thatsubstantially all of the patient's weight applied through the patient'sleg stump to the first end portion is supportable through thecompressible medium, wherein the compressible medium is compressedduring heel strike of the prosthetic foot and is decompressed when thepatient's weight shifts during movement of the prosthetic foot; and abearing interposed between the first and second end portions such thatit restricts the decompression of the compressible medium until anappropriate moment in the movement of the prosthetic foot when thedecompression will assist the patient in accelerating forward.
 15. Thepylon of claim 14 wherein one of the first and second end portionsincludes a piston having a head, wherein the other of the first andsecond end portions includes a piston chamber for receiving the pistonalong the longitudinal axis of the pylon, wherein the compressiblemedium is enclosed by the piston head and piston chamber, wherein thebearing comprises a wear band interposed between sides of the piston andinterior walls of the piston chamber such that it momentarily restrictsrelative motion between the piston and the piston chamber along thelongitudinal axis of the pylon when a sufficient moment is imparted tothe piston relative to the piston chamber about a lateral axis of thepiston during the movement of the prosthetic foot.